1. Technical Field
Embodiments of the invention relate generally to internal combustion engines, and more particularly to turbocharged engines. Other embodiments relate to diesel engines with multi-stage turbocharger arrangements.
2. Discussion of Art
Ships typically carry two types of diesel engines: main propulsion engines and auxiliary engines. Both types of engine generate emissions of PM 2.5 (diesel soot), SO2 (sulfur dioxide), and NOx (nitrous oxides). Some governmental agencies, however, have adopted standards that will limit engine emissions, particularly NOx. For example, some of these standards apply to engines installed on U.S. vessels and to marine diesel fuels produced and distributed in the United States.
NOx emissions vary according to engine speed, combustion temperature, and the quantity of fuel burned. Lower speeds and higher combustion temperatures tend to raise the amount of NOx produced per quantity of fuel burned. As will be appreciated, low speed and high combustion temperature can be desirable characteristics of high-load internal combustion engines such as marine diesel propulsion engines. Therefore, the simplest path for reducing NOx emissions is to reduce the quantity of fuel burned per unit of useful power.
Turbochargers can be useful for enhancing fuel efficiency of piston-cylinder engines, by augmenting the mass and pressure of air inhaled into each cylinder during its intake stroke. However, turbochargers for marine diesel engines can be difficult to fit into the machinery space provided for the engines and their interfacing equipment.
As will be appreciated, it is desirable to minimize the machinery space within large ships, which are built to carry cargo. Therefore, it is desirable to provide a marine diesel turbocharger arrangement that satisfies enhanced emissions standards while not requiring excessive machinery space.